1. Field of the Invention
The present invention relates to a wire harness for interconnecting electric members arranged at a distance from each other in various apparatuses such as electric devices, motor vehicles and the like, and a lighting device, a backlight device, and a liquid crystal display device that are suitable for supplying alternating-current power using the wire harness.
2. Description of the Related Art
In the past, wire harnesses have often been used in a lighting device, a backlight device, and a liquid crystal display device as electric devices and various apparatuses such as motor vehicles and the like. A wire harness is to interconnect electric devices, electric parts, or electric blocks (which will hereinafter be referred to generically as electric members) arranged in a state of being physically separated from each other, so that electric signals or power is exchanged between these electric members. That is, a wire harness includes a set of one or a plurality of wires whose length, bend shape and the like are predetermined. A wire harness shortens a time for connecting electric members to each other during manufacturing of the above-described various devices, prevents erroneous wiring, and uniformizes wiring routing to improve product quality.
In a field of electric devices, in particular, there has recently been a sign of rapid spread of liquid crystal display devices into general households. Such a non-self-luminous display device uses a backlight device formed by providing a backlight unit (lighting unit) using a cold cathode fluorescent tube as a light source and interconnecting the lighting unit and a drive and control unit for driving the lighting unit by a covered wire made of a conductive material. Also, cold cathode fluorescent tubes driven at a high frequency than the frequency of commercial power have been coming into use as a lighting device for illumination because of good efficiency of light emission of the cold cathode fluorescent tubes.
Such backlight devices having a lighting unit and a drive and control unit and lighting devices for illumination light a cold cathode fluorescent tube using alternating-current power at a few ten kHz in many cases. Techniques such for example as a technique of supplying power from one cold cathode fluorescent tube driving device to a plurality of cold cathode fluorescent tubes by a conductive material wire (see Japanese Patent Laid-Open No. 2002-303848, referred to as Patent Document 1 hereinafter) and a technique for reducing leakage current from a covered wire using an insulating material for a casing (see Japanese Patent Laid-Open No. 2001-255527, referred to as Patent Document 2 hereinafter) have been actively studied.
In a field of motor vehicles, electric vehicles using a synchronous motor are drawing attention. Also in this field, a covered wire for connecting the synchronous motor and a control unit may be required, a current flowing through the covered wire is an alternating current, and a leakage current occurs as in the backlight devices of liquid crystal display devices and lighting devices for illumination as described above.
It is desirable to use a wire harness in the backlight device of a liquid crystal display device as described above in order to improve mass productivity. Recently, on the other hand, the screen of the liquid crystal display device has become larger, the backlight device has accordingly become larger, and power for driving cold cathode fluorescent tubes has been increasing. Further, the use of a mode in which one inverter circuit (drive and control unit) sequentially drives a plurality of cold cathode fluorescent tubes or simultaneously drives the plurality of cold cathode fluorescent tubes, as disclosed in Patent Document 1, has been increasing. As a result, the wire harness becomes longer as compared with a case where one cold cathode fluorescent tube is driven by one inverter circuit. In a lighting device for illumination, a cold cathode fluorescent tube and a driving power unit are separated at a distance in order to increase design freedom. In the field of motor vehicles, a distance between a driving power unit and a synchronous motor operating on alternating-current power is increasing because of use of a so-called in-wheel motor. In either case, the wire harness for connecting the driving power unit and a load circuit to each other tends to become longer.
In such a case, a wire harness as used in the past in an electric device, a motor vehicle or the like, the wire harness being made by only forming a bundle of covered wires along a wiring path, increases an absolute amount of leakage current flowing to a conductive material casing (for example an iron or aluminum chassis), so that power from a drive and control unit does not efficiently reaches a load circuit such as a cold cathode fluorescent tube or the like. This for example invites a decrease in light emission efficiency or an increase in size of the drive and control unit in the backlight device, and further invites an increase in unnecessary device power consumption. Using an insulating material for a casing as disclosed in Patent Document 2 can reduce leakage current, but has problems to overcome in terms of the strength of the casing and measures against undesired electromagnetic radiation. Incidentally, lighting devices for illumination and electric vehicles have similar problems to solve as power is increased and as alternating-current power frequency is raised.
In view of the above problems, it is desirable to provide a wire harness that causes a small amount of leakage of alternating-current power and is suitable for supplying alternating-current power, and a lighting device, a backlight device, and a liquid crystal display device that supply alternating-current power using the wire harness.